It is one of nature’s most spectacular displays; now scientists have shown how chameleons change colour.

A study has found that the lizards possess a layer of skin cells that contain floating nanocrystals. The tiny crystals are more or less evenly spaced throughout the cells and this spacing determines the wavelength of light that the cells reflect.

The latest research shows that chameleons switch colour from green to red by actively changing the spacing between these tiny cellular crystals.

Professor Michel Milinkovitch and his team at the University of Geneva in Switzerland cracked the problem after years of studying the panther chameleon (Furcifer pardalis), a native of Madagascar.

When a male encounters a male competitor or a potentially receptive female, it shifts the background colour of its skin from green to yellow, its blue patterning turns white and the red markings becomes brighter.

“This happens within minutes of it seeing another male,” said Milinkovitch.

In the study, published in the journal Nature Communications, the scientists studied the skin of the lizards using spectroscopy.
They found that, beneath several layers of pigmented skin cells, the chameleons have a layer of cells called iridophores, containing nanocrystals made of guanine, one of the four key components of DNA.

The guanine nanocrystals are arranged in a lattice throughout the cell, the spacing of which determines the cell’s colour. When the chameleon is calm, the crystals were found to be organised into a dense network, reflecting blue wavelengths most strongly. When excited, the chameleon was found to loosen its lattice of nanocrystals by about 30%, allowing the reflection of yellows or reds. “They’re basically pulling apart or squashing together the lattice,” said Milinkovitch.

The scientists have yet to work out how chameleons cause this change, but it could be because cells shrink or expand, giving the crystals more or less space to fill.

Previously scientists had shown that chameleons are also able to change their colour with the migration of melanin in and out of cells, turning them from pale to dark green, for instance.